This invention has been created without the sponsorship or funding of any federally sponsored research or development program.
This invention relates generally to the field of mass spectrometry and more particularly toward sample substrates having a surface for reduced interaction with reactive samples and laser radiation.
There are several surface ionization techniques that are useful in mass spectrometry (hereinafter referred to as MS). Types of surface ionization include, but are not limited to, fast ion or atom bombardment, field desorption, laser desorption, plasma desorption. This technique is described more fully in U.S. Pat. No. 5,118,937 of Hillenkamp et al. and U.S. Pat. No. 5,777,324 to Hillenkamp. One of the most widely used surface ionization techniques utilizes matrix assisted laser desorption ionization (hereinafter referred to as MALDI). One of the problems of the MALDI technique is the cleanliness of the sample as well as its interaction with a substrate, which can have an influence on the sample crystallization process. For example, presence of sodium at the surface of the substrate can easily contaminate the sample to produce distorted spectra. Interpretation of this distorted data is somewhat more difficult. Also higher ionic contents on the surface of the substrate can negatively affect the sensitivity of the technique by decreasing the ion yield for the sample. Also surface reactivity is a concern with reactive samples. Ideally, the sample should stay intact during the analysis. For example, gold plated substrates commonly produce satisfactory results. Also there were several attempts to use stainless steel and amorphous silicon as sample substrates.
A variation of the MALDI technique involves the elimination of the matrix and the introduction of a sample substrate surface which reacts with the sample. An example of this modified MALDI technique is illustrated in U.S. patent of Siuzdak et al. U.S. Pat. No. 6,288,390. This patent describes a porous light-absorbing semiconductor substrate. The patent describes an extensive list of light absorbing materials. When the source of radiation irradiates the substrate under reduced pressure and an analyte from the sample is absorbed on the substrate, the irradiation also causes the desorption and ionization of the analyte. Although this technique eliminates the need for a matrix, the substrate must be replaced after limited use.
These and other difficulties associated with laser desorption/ionization techniques for mass spectrometry, with and without the use of matrix, have been obviated by the present invention.
It is, therefore, a feature of the present invention to provide an apparatus for spectroscopic analysis which utilizes the MALDI technique and which includes a sample substrate that is chemically inert to the material in the sample to be analyzed and to the materials in the matrix with respect to sample degradation and contamination at the substrate.
Another feature of the invention is to provide a sample substrate for an analyzer using MALDI that is relatively electrically conductive and non light absorbing.
A further feature of the invention is to provide a sample substrate for an analyzer using MALDI that has mechanical hardness and resists sample penetration into the substrate surface during application of the sample to the surface and irradiation by the laser.
Still another feature of the invention is the provision of a sample substrate that is easy to clean and which can be reused for many sample cycles.
Another feature of the invention is the provision of a sample substrate that is inexpensive and that can be treated as disposable, offering, for example, an inexpensive way for archiving a portion of the sample by archiving it with the substrate.
The present invention relates to an apparatus and method for use with a mass spectrometer (MS) or MS system with MALDI. The substrates of the present invention have a surface for reduced interaction with sample and comprises a surface having an inorganic, conductive nitride compound which is at least a major amount by weight from the group of titanium nitride, zirconium nitride and hafnium nitride. The nitride compound may be, for example, a mixed metal nitride such as an aluminum titanium nitride or chromium-titanium-nitride. Titanium-carbon-nitride may also be used.
The invention also provides a method of producing a substrate surface having reduced interaction of a reactive sample. The method comprises applying a coating to a substrate body selected from the group consisting of titanium nitride, zirconium nitride and hafnium nitride of metals to the surface of the substrate.
The invention also relates to a MALDI apparatus for providing an ionized sample of material to an analysis instrument that includes the improved substrate of the present invention. The invention further relates to a mass spectrometer that includes the substrate of the present invention with MALDI apparatus for providing an ionized sample of material to the mass spectrometer.